Brake



May 8, 1945. w. s-TELzERa ,375,392.

BRAKE 7 Filed Jan. 16, 1.945

uymvfok.

Patented May 8, 1945 Application Jittery) 1c, 1943, lain. amen 5 "The invention relates to brakes and moreparticu'larly to a brake ofthetorque-rea'ctivetype where the friction members have no anchor point I to engage the-friction members with the brake the principle in a simple construction that lends itself particularlyfor use with air or mechanical brakes'where the actuating force must be transmitted through a'rotating shaft.- 1

Another object is to "provide means for trans- Initting the brake torque from one shoe to the other, as well as novel meansfor equalizing'the brake drum.

pressures between the "friction surfaces and -the -Other objects and'advantages of this invention willbeapparent from the "following detaileddescription considered in connectionwith the accompanying drawing submitted for the purpose" of illustration and not to define the scope ofthe invention, reference being had for that purpose to thesubjoined claims. "In the drawing, wher'ein throughout the several viewsz v, i

I Fig. 1 is a diagrammatic side elevation .of. a brake built according to the novelprinciple, wherethe brake drum is shown in section to similar reference characters refer to similar parts.

provide an unincumbered'view of the brake struction;

Fig. '2, a diagrammatic sidee levation showing a the invention embodied in an external brake;

n Fig. 3, a fragmentary side elevation of a modified form of the invention, wher thelower'portion may be similar to theillustration inFig. 1.

Before explaining'the present invention inde-j tail, it isto be understood that the .invention'is not limited in its application to the detailsof construction and arrangement of par.ts 'illus' trated in the accompanyingdrawing, since the invention is capableof other embodiments and of being practised or carried out in various ways.

Also it is to be understood that the phraseology 9 or terminology employed herein is for the purpose of description and not limitation.

Referringnow to Fig. 1, there is shown an embodiment incorporated in a wheel of an automotive vehicle where I represents the backing plate rigidly secured .:to the axle, and 2 the. brake drum, whichrevolves with thewheel. Arranged nearthebrake drum are a pair of internal brake shoes =3 and l-urged -in ,a're1eased position"by retraction springs '5 to rest' against' stop pins-6 extending from --back-ing plate I.

ble inwbac'kin'g plate *A lever *ll extendsrfrom shaft J0 to beengaged b -a'-brake rod 12 actuated byaa brake .pedal l=3 operatable by the operator, ,whereby depression of" pedal I 3 turns double armed lever l-0. Leverll may also be connected to a rod M leading-to a conventional expansible chamber-motor mechanism 15 controlled byfluid pressure means.-

' "In contrast to conventional brakes :the brake I shoes -3 and 4 have-nofixed anchor The shoes are merelyli-nked together by means 'of' "toggle links lfi andfllvpivotally joined together at ll to form a knee'which can slide'on plate IB-secured tobac'kingplate I. 'Dueto this con? struction I the torque: reaction is taken up entirely by lever 9 and transmitted to shaft lo andthe backing plate;

-- a In Fig. 2 thprinciple is applied to 'anexternal; type brake having a -brak'e-d-r'um or brake wheel 19 around which ie-Wrapped a brake bandit} pivoted at 2lto'a double armed lever 22 turning I on a fixed anchor'stud' 23,"operated by a'rod12'4 which may'be theequivalent ofrod 12 or14 .1-A connecting rod -2 5"links lever 22 and the-other I 'endof shoe so that whenrod 24 is pulled to 1 the right the shoe is engagedv with the drumi In order to limit 'the self-energizing-efiect of the.

band, it is: preferable to' 'give it certain rigidity which gives'it a tendency to unwrap.

internal brake,"similar to Fig.

Fig. 3 shows a-modification pertaining to an In place "of shaft l0 there, is shown a fixed anchor stud 26 ext'endingfrom backing plate'zl, serving asafulcrum for lever '28 actuated byga fluid motor mechanism consisting of a piston 29' and a cylinder 30in connection with the con: ventional" brake line 3 l leading to the master cylinder or the like; .Actuatorlever .28 ,is pivotally connected with shoes 32 and 33 by means of'1inks34'and35.

In operation, supposing that the operator de- 1 presses brake pedal l3 he thereby actuates double armed lever 9 in a clockwise rotation to expand 1 the brakeshoes until they press againstthe brake drum. Assuming that the latter ordinarily revolves in a direction indicatedby arrow 36, the brake torque or drag due to the friction between The toes use I 8 of thebrake shoes engage th'e-endsof a double 1 armed lever .or cam s liav-i-ng a shaft l-ll "revolva lj, t

the shoes and the drum is transmitted to lever 9 1 where the end 8 contacts it. The upper extremity of shoe 3 is the energizing. end from wherej 1 pedal.

through the center of shaft I ll.

obliquity the outward radialforce of the shoe 3 at I creased. 9

of .the'vehicle, the wear or the shoes while the vehicle is backing up is of no consequence.

the brake torque builds up. Thebrake torque acting at 8 depends on the comparatively small: force acting at I, and is1greatly' increased due. to the self-energizing action of the fSheS,-Whi0h"' r in turndepends on the 'coeflicient of friction of the brake shoes. By inspection "of the drawing 1 it becomes apparent that the. brake torque causes a reaction opposing ,thefdepression,ofthe brake Thus the greater the braketorque the greater must be the manual pressure on pedal l3 to maintain that brake torque. This is a;veryj may be illustrated by assuming that the brake torque is momentarily too great. The increased reaction opposing the depression of pedal l3 causes the latter. to yield so that lever 9. turns in a counterclockwise rotation, the brake shoes being able to rotate with drum 2 a short distance.

Since, lever 9 turns counterclockwiseand shoe3 moves awayfrom it, the pressure of lever 9 on;

shoe 3.is reduced, resulting in a reduction of iriction between the shoes andthe drum, and consequently a reduction of the brake torque. It is ap-.,,

Parent that the reduction of the brake torque only takesQplace while it exceeds the inherent ratio of pedal. pressure to brake torque, and since the brake torque may be changed merely by changing the pressure betweenlever 9 andltip I, it maybe seen that the movement necessary is a minimum and is not noticeable by the operator; M

'The brake torque produced by shoe 3 is transmitted through links l6 and Hi to shoe 4 to press Supposing that the operator releases the foot pressure on the pedal, the torque acting through tip 8 against lever 9, as wellas the force of re.- turnsprings 5 urge the shoes and the actuating elements into a released position as shown in Fig. 1.

The operation of the construction shown in Fig. 3,. is similar "to that described for Fig.1. The actuation being hydraulical, apressure produced in brake line3l moves piston 29 to'turn lever 28 in a clockwise direction, whereby the links 34 and transmit the force of application to the brake shoes. Link 35 receives the brake torque, and 34 produce the same result as the oblithe upper end of shoe 32is urged with increased force against the drum, and the brake torque from shoe 33 is transmitted through link 35 to produce a force, component that urges a decrease of pres- ,sure between the upper. end of shoe 33 and; the

drum. The operation of the modified construction shown in Fig. 2 is self-explanatory. ,The normal direction of rotation of the drum where the'linings by arrow 31. 1

wear most evenly isindicated Having thus described my invention, I claimj 1. In a brake, afixed backing plate, a revolving brake drumQa pair of brake shoes circumferen tially arrangednear said-brake drum, a toggle joint between two adjacent ends of said brake shoes to transmit the brake torque from one shoe the latter with increased force against the drum.

While thistype of self-actuationprovides ease of application, it causes uneven wear of the shoes because the pressure between the shoeand the, drum increases as the, brake torque increases;-

thus the wear is greater where the torque is trans-1 mitted to lever 9, and smallest where the shoe is first applied. To prevent this uneven'wear I provide the means as shown in the drawing. The

principle is to increase the radial pressure where lever comprises a hydraulicwheel cylinder operthe torque is small, and to reduce it where the torque is great. :Links {6 and I6: not only trans- Lever 9 is arranged in such a way that when it is applied the fiat surfaces engaging the shoes form an oblique line with respect to'a radial line drawn Due to this its upper end isincreased and jon shoe .4 it is de} While the, elements. may be arranged, as e lscribed. to provideeven wear of the brake shoes,

. 3 the benefit is obtained only when the drum rotates asindicated by arrow 36. j However, since this may be the rotation of the wheel during forwardtravel mit the torque from one shoe to the other but they M also produce a resultant force opposing the radial pressure between the brake lining and the drum.

to the other, the knee of said toggle oint sliding on a surface extending from said backing plate, saidknee pointing outwardly whereby the radial pressure of said brake shoes near'said to gle joint is reducedwhen torque is transmitted, a double they end of one brake shoe to urge it against said brake drum, and the other arm of said lever being connected to the adjacent endIof the other brake shoe to receive the brake torque, and' means operatesaid doublearmed lever.

. 2. The construction as claimed in' claimf l,

where said means to operate said double armed able by hydraulic'fluid. I

3. In abrake, a fixed backing plate, a, revolving brake drum',,a pair of brake shoes circumferen tially arranged near said drum, afljoint between two adjacent ends of said brake shoes to transmit the brake torque from one shoe to the other, a double armed lever intermediate the other two adjacent ends of said brake shoes, the fulcrum ofsaid lever being in fixed relation to saidbacking plate,,one arm of said lever being operatively linked to the energizing end of one brake shoe in a manner to urge it against said brake drum, and a link between the other arm of said levera nd the torque transmittingheeliof the brake shoe ar-.

rangedina manner to decrease the radial force of said shoe against'said drum,

WILLIAM STELZER.

energizes shoe 32.- The two links mentioned are arranged to quity of the contact surfaces of lever 9, whereby armed lever intermediatethe other two adjacent ends of said brake shoes, the fulcrum of said lever being in fixed relation to said backing plate, one armof saidlever being operatively connected to 

